A gas turbine plant includes for example a compressor and a combustion chamber, as well as a turbine. The compressor provides for compressing intake air with which a fuel is then mixed. Combustion of the mixture takes place in the combustion chamber, with the combustion exhaust gases being passed to the turbine. There, heat energy is taken from the combustion exhaust gases and converted into mechanical energy.
Fluctuations in the quality of the fuel and other thermal or acoustic disturbances however result in fluctuations in the amount of heat liberated and thus the thermodynamic efficiency of the plant. In that situation, there is an interaction of acoustic and thermal disturbances which can push themselves up. Thermo-acoustic oscillations of that nature in the combustion chambers of gas turbines—or also combustion machines in general—represent a problem in terms of designing and operating new combustion chambers, combustion chamber parts and burners for gas turbines or combustion machines.
The exhaust gases produced in the combustion process are at a high temperature. They are therefore diluted with cooling air in order to reduce the temperature to a level which is tenable for the combustion chamber wall and the turbine components. The cooling air passes into the combustion chamber through cooling air openings in the combustion chamber wall. In addition so-called seal air passes into the combustion chamber, that is to say, air which serves to prevent the entry of hot gas from the combustion chamber into gaps between adjacent elements of a heat-protective lining of the combustion chamber. In that case the seal air is blown through the gaps between adjacent elements of the heat-protective lining into the combustion chamber.
Diluting the combustion gases with cooling and seal air however results in a higher level of pollutant emissions. In order to reduce the pollutant emissions of gas turbines, the cooling and seal air flows are therefore kept low in modern plants. As a result however that also reduces the acoustic damping effect so that thermo-acoustic oscillations can increase. That can involve a mutually increasing interaction between thermal and acoustic disturbances which can cause high levels of stress and loading for the combustion chamber and increasing emissions.
Therefore, in the state of the art, for the purposes of reducing thermo-acoustic oscillations, for example Helmholtz resonators are used for damping thermo-acoustic oscillations in combustion chambers of gas turbines, which damp the amplitude of the oscillations.
In order to be able to damp the thermo-acoustic oscillations in a greater frequency range, DE 33 24 805 A1 proposed using a plurality of Helmholtz resonators involving different resonance frequencies, which are arranged laterally at the air passage to the combustion chamber. In that case each Helmholtz resonator damps different frequencies of the acoustic oscillations. It will be noted that cooling air has to be additionally used. That either increases the cooling air consumption, or it means that less cooling air is available for cooling the combustion exhaust gases, whereby there is an increase in the proportion of pollutants in the combustion exhaust gases.
Therefore there is a need for a combustion chamber and a gas turbine in which the arrangement of different damping devices is such that the additional cooling air requirement can remain relatively low.